To reduce the cost and increase the performance of electronic computers, it is desirable to place as many electronic circuits in as small a region as possible in order to reduce the distance over which electrical signals must travel from one circuit to another. This can be achieved by fabricating, on a given area of a semiconductor chip, as many electronic circuits as feasible with a given fabrication technology. Typically, these dense chips are disposed on the surface of a substrate in a side by side arrangement with space left therebetween to provide regions for electrical conductors for electrical interconnection of the chips. The chip contact locations can be electrically connected to substrate contact locations by means of wires bonded between the chip contact locations and the substrate contact locations. Alternatively, a TAB (Tape Automated Bonding) tape (which is a flexible dielectric layer having a plurality of conductors disposed thereon) can be used for this electrical connection. Alternatively, the semiconductor chips can be mounted in a flip-chip configuration wherein an array of contact locations on the semiconductor chips is aligned with and electrically connected to an array of contact locations on the substrate by means of solder mounds disposed between corresponding chip and substrate contact locations. The side by side arrangement of electronic devices is not the most dense configuration which can be achieved.
The most dense packaging configuration for semiconductor chips, in particular for memory chips, such as DRAMs SRAMs, Flash EEPROMs and the like, may be obtained through the construction of a cuboid structure of semiconductor chips. The difficult problems to solve for such a cube are providing for electrical connections to the chips, dissipating heat and reworking bad chips. The electrical connections must include power supply, data and address lines and the like.
Prior art shows that it is possible to construct dense packages of stacked semiconductor wafers or chips. The major problems are that of interconnecting the chips electrically and that of solving the problem of thermal dissipation. Chips are generally stacked in orthogonal rectangular or cuboid structures.
Generally, the problem of thermal dissipation is either not addressed or is handled by conduction through the structures to the environment.
The trend in the electronics industry is to package. One approach is to package the chips in a 3-D form factor in which the input and output lines of the chips are brought to one edge of the chip and then multiple chips are glued together to form a cube. Since the chips in the cube are permanently bonded together, it is very difficult to rework. The current technology of doing single-chip test and burn-in is also not compatible with this type of cube packaging.
U.S. Pat. No. 5,031,072 describes making a baseboard for orthogonal mounting of integrated circuit chips. Plural channels are anisotropically etched in a silicon baseboard and a plurality of chips are inserted into the channels. A number of baseboard contact pads are formed adjacent to each channel and are solder bonded to corresponding chip conductor pads. The base board is made of rigid silicon and it requires that a chip must have conduction pads near its edge for bonding to the baseboard. Also, the base board must have channels for the chips to be inserted and thus, the interconnection wires on the baseboard must be routed around the channels. As a result the average length of signal wires is thus longer than desired and the baseboard substantially wider than the footprint of the chips mounted to it.
U.S. Pat. No. 5,037,311 describes an interconnect strip to provide electrical interconnection between a plurality of conductor pads disposed on a plurality of circuit boards. The strip can be fabricated from a polymer film carrier having disposed on both sides thereof, a metal foil with preselected spring properties formed into electrical conductors which have ends which cantilever off two opposed edges of the film. Some of the ends are inserted into slots in the circuit boards to locate the remaining adjacent contact locations on the circuit boards.
U.S. Pat. No. 5,041,903 describes a structure of a tape frame for Tape-Automated-Bonding (TAB) packages. Chips are mounted onto TAB lead frames, a portion of the leads are parallel to the chip and a portion (the outer lead end) of the lead is formed (bent) to allow the tape to be outer lead bonded to a substrate so that the package can be mounted at any desired non-zero angle with respect to a substrate. The bent portion of the outer lead is soldered to a substrate. The bent portion limits the spacing between adjacent packages to approximately between 50 and 150 mils which is the length of the bent outer lead needed to form a solder bond to the substrate.
U.S. Pat. No. 2,568,242 is directed to a method of using a solder filled wire having a core of a metal member to store solder in solid form before joining it to another metal member. The member is subsequently sheared so as to place the solder into a non-equilibrium state with the excess solder facilitating a subsequent solder connection to a nearby metal surface.